To be fair both could have connections of being Family while dealing with 'Animatronics' I put quotes cause while Finn, Alex, and Jeremy do face Animatronics their also ones based off each other.
If this fight happens then I could go more in depth to explain.
It could also be a fight of Traumtized kids/teenagers considering the shit the Animatronics have caused a bunch of Teens to go through trauma. Finn, Alex, and Jeremy. The whole Rayner trying to take over the world would cause that along with an all out Hero/Villian War
They are also on this like humongous group (Freddy, Bonnie, Chica, and Foxy belonging to The Anomatronic group while Finn, Alex, and Jeremy belong to the well over 20+ friend group of Tom)
-All Combatants are people who've dealt with Robots that looked just like them with only slight changes and had the destroy them (Freddy and his Gang with the Twisted One's and Finn, Alex, and Jeremy with their Evil clones)
-It can be a battle of Kids vs Teenagers
-All 7 of them also come from a huge group of Friends (Freddy and the gang with The Animatronics and Finn, Alex, and Jeremy with Tom and the group they call The New Warriors
-It could also eventually become a sort of Fathers bs Children battle as Finn, Alex, and Jeremy have a kid and become dads while the Animatronics are possesses with the souls of Kids so it's a sort of Opposites battle.
-They also become a sort of older generation for their future to look back at (The Original Gang with Animatronics such as the Rockstar Animatronics and Finn, Alex, and Jeremy with their Kids)